Storage system for components incorporating a liquid-metal thermal interface

ABSTRACT

Embodiments of an apparatus that functions as a storage system for components are described. This apparatus includes a containment vessel enclosing a desiccant and a device. This device includes a layer mechanically coupled to a component, where the component can be one of a semiconductor die and a heat-removal device. Moreover, a thermal-interface material is coupled to a region of the layer, and a boundary material is mechanically coupled to the layer, where a perimeter defined by the boundary-material surrounds the region.

BACKGROUND

1. Field of the Invention

The present invention relates to system for storing and protectingcomponents. More specifically, the present invention relates to a systemfor storing and protecting components that includes a liquid-metalthermal-interface material.

2. Related Art

The functionality, performance, and operating speed of integratedcircuits (ICs) have increased significantly in recent years. This hasresulted in significantly increased power consumption and associatedheat generation in these devices. Consequently, it is becoming aconsiderable challenge to maintain acceptable internal and externaloperating temperatures in these ICs.

One approach to managing the increasing thermal load is to use animproved thermal-interface material between a semiconductor die in an ICand an external environment (such as the IC package). Proper operationof the semiconductor die over a range of operating conditions determinesseveral required properties for a candidate thermal-interface material.In particular, the thermal-interface material should not containimpurities and should not damage the semiconductor die. Moreover, thethermal-interface material should have a high bulk thermal conductivityand should conform to a surface of the semiconductor die at ambient orlow pressure, thereby ensuring a low thermal impedance between theexternal environment and the semiconductor die.

Several liquid metals are promising candidates as improvedthermal-interface materials. In principle, these liquid metals canprovide the required properties, if the liquid metals are dispensed in acontrolled manner. However, it is often difficult to work with liquidmetals. For example, liquid metals do not wet with many materials.Consequently, it may be difficult to fabricate a thin layer of liquidmetal that conforms to the surface of the semiconductor die. Moreover,many liquid metals are highly corrosive and/or dissolve other metals,which makes them extremely difficult to handle during manufacturing,thereby increasing the complexity and the cost of the manufacturingprocesses, which may prevent the use of these improved thermal-interfacematerials.

Hence what is needed are techniques for handling and protectingcomponents that include liquid metals without the problems listed above.

SUMMARY

One embodiment of the present invention provides an apparatus thatincludes a containment vessel enclosing a desiccant and a device. Thisdevice includes a layer mechanically coupled to a component, where thecomponent can be one of a semiconductor die and a heat-removal device.Moreover, a thermal-interface material is coupled to a region of thelayer, and a boundary material is mechanically coupled to the layer,where a perimeter defined by the boundary-material surrounds the region.

In some embodiments, the apparatus includes an exterior containmentvessel enclosing the containment vessel. Moreover, another desiccant maybe included within the exterior containment vessel but outside of thecontainment vessel.

In some embodiments, the thermal-interface material includes a materialthat is a liquid metal over a range of operating temperatures of thesemiconductor die.

In some embodiments, at least one of the layer and an inner surface ofthe boundary material includes a material that is resistant to corrosionby the thermal-interface material. For example, the material may includea metal, such as nickel, a nickel alloy, and/or stainless steel.Moreover, at least one of the layer and the inner surface of theboundary material may include a material which has a water permeabilitythat is less than a pre-determined value.

In some embodiments, the layer is deposited and/or adhered onto thecomponent.

In some embodiments, the boundary material is mechanically coupled tothe layer by grease.

In some embodiments, the semiconductor die includes a processor.

In some embodiments, the thermal-interface material includes agallium-indium-tin alloy.

Another embodiment of the present invention provides another apparatusthat includes a layer mechanically coupled to a component, and anotherlayer mechanically coupled to another component. Note that the componentcan be one of a semiconductor die and a heat-removal device, and theother component can be a dummy component. Moreover, a thermal-interfacematerial resides between the component and the other component, wherethe thermal-interface material is mechanically coupled to a region ofthe layer and to a region of the other layer. Additionally, a boundarymaterial is mechanically coupled to the layer and the other layer, wherethe thermal-interface material is contained in a cavity defined, atleast in part, by the layer, the boundary material, and the other layer.

In some embodiments, a desiccant is included within the cavity.

In some embodiments, the thermal-interface material includes a materialthat is a liquid metal over a range of operating temperatures of thesemiconductor die.

In some embodiments, at least one of the layer, the other layer and aninner surface of the boundary material includes a material that isresistant to corrosion by the thermal-interface material. For example,the material may include a metal, such as nickel, a nickel alloy, and/orstainless steel. Moreover, at least one of the layer, the other layerand an inner surface of the boundary material may include a materialwhich has a permeability for water that is less than a pre-determinedvalue.

In some embodiments, the layer is deposited and/or adhered onto thecomponent.

In some embodiments, the boundary material is mechanically coupled tothe layer and the other layer by grease.

In some embodiments, the semiconductor die includes a processor.

In some embodiments, the thermal-interface material includes agallium-indium-tin alloy.

In some embodiments, the other apparatus includes a containment vesselenclosing the apparatus and another desiccant within the containmentvessel.

BRIEF DESCRIPTION OF THE FIGURES

FIG. 1 is a block diagram illustrating a chip package in accordance withan embodiment of the present invention.

FIG. 2A is a block diagram illustrating a portion of a process forapplying a thermal-interface material in accordance with an embodimentof the present invention.

FIG. 2B is a block diagram illustrating a portion of a process forapplying a thermal-interface material in accordance with an embodimentof the present invention.

FIG. 2C is a block diagram illustrating a portion of a process forapplying a thermal-interface material in accordance with an embodimentof the present invention.

FIG. 2D is a block diagram illustrating a portion of a process forapplying a thermal-interface material in accordance with an embodimentof the present invention.

FIG. 3 is a block diagram illustrating a mask for use during a processfor applying a thermal-interface material in accordance with anembodiment of the present invention.

FIG. 4 is a block diagram illustrating a chip package in accordance withan embodiment of the present invention.

FIG. 5A is a block diagram illustrating a storage system for componentsthat incorporate a liquid metal in accordance with an embodiment of thepresent invention.

FIG. 5B is a block diagram illustrating a storage system for componentsthat incorporate a liquid metal in accordance with an embodiment of thepresent invention.

Note that like reference numerals refer to corresponding partsthroughout the drawings.

DETAILED DESCRIPTION

The following description is presented to enable any person skilled inthe art to make and use the invention, and is provided in the context ofa particular application and its requirements. Various modifications tothe disclosed embodiments will be readily apparent to those skilled inthe art, and the general principles defined herein may be applied toother embodiments and applications without departing from the spirit andscope of the present invention. Thus, the present invention is notintended to be limited to the embodiments shown, but is to be accordedthe widest scope consistent with the principles and features disclosedherein.

Embodiments of an apparatus that includes a thermal-interface materialare described. This apparatus may be assembled during a manufacturing orfabrication process. During the process, surfaces on one or morecomponents in the apparatus, such as a heat-removal device and/or one ormore semiconductor dies, may be prepared, for example, by depositing oneor more layers and/or by adhering one or more films to these surfaces.These layers and/or films may include materials that are compatible withthe thermal-interface material. In particular, the materials may haveproperties that prevent the thermal-interface material from damaging thecomponents and which facilitate a low thermal boundary impedance betweenthe thermal-interface material and a given surface. For example, one ofthe materials may be substantially insoluble in the thermal-interfacematerial and another of the materials may wet the thermal-interfacematerial.

Next, one or more regions may be defined on one or more of the surfaces,for example, by adhering a mask (such as a contact mask) onto the givensurface. Then, the thermal-interface material may be applied, forexample, by using a spray-coating technique.

Note that the one or more semiconductor dies may include a processor,and the heat-removal device may include: a heat sink (which may be madeof a metal such as copper), a Peltier device, a liquid-cooled coldplate, and/or a thermal reservoir. Moreover, the thermal interface mayinclude a metal in a liquid state (or more generally, a metal alloy) asa thermal-interface material. This metal or metal alloy (henceforthreferred to as a liquid metal) may have a low melting point (such asbelow room temperature or 25 C). More generally, the liquid metal has amelting point which is below an operating temperature of thesemiconductor die.

In an exemplary embodiment, the liquid metal includes gallium, indium,and tin. Note that the liquid metal may also include elements other thanmetals, such as diamond or graphite.

Moreover, during assembly of the apparatus a boundary material (such asa metal-coated gasket) may be mechanically coupled and/or chemicallycoupled to the semiconductor die and the heat-removal device, therebydefining a cavity that includes the thermal-interface material. Whenassembled, the thermal-interface material may be mechanically coupledand/or chemically coupled to regions in layers or films on thesemiconductor die and the heat-removal device, which may include atleast one of the previously described materials or another material. Forexample, these layers may include a material that is resistant tocorrosion by the thermal-interface material and/or a material which hasa permeability for water that is less than a pre-determined value.

In some embodiments, the boundary material is mechanically coupledand/or chemically coupled to the semiconductor die and the heat-removaldevice by grease. Moreover, the apparatus may include a desiccant in thecavity.

In some embodiments, a service kit is used to store and protectcomponents, such as the semiconductor die and/or the heat-removaldevice, after an intermediate operation during the assembly process(such as after the thermal-interface material is applied). This servicekit may include one or more containment vessels (such as an internalcontainment vessel and an external containment vessel), each of whichmay include a desiccant. For example, the semiconductor die,thermal-interface material and the boundary material may be containedwithin the one or more containment vessels. Moreover, a dummy layer maybe coupled to the boundary material to complete the cavity surroundingthe thermal-interface material within the internal containment vessel.

In the discussion that follows, a semiconductor die is understood toinclude: a bare die, a packaged die, multiple die, and/or two or moredie in a single package (which is sometimes referred to as a multi-chipmodule).

By including the boundary material and thus defining the cavity, whichisolates or contains the liquid metal and protect the liquid metal fromcontamination, the apparatus may facilitate the use of the liquid metalas a thermal-interface material. Moreover, the liquid metal may improvethermal coupling between the heat-removal device and the one or moresemiconductor dies. In particular, the liquid metal may facilitate a lowthermal impedance between the one or more semiconductor dies and theheat-removal device. In an exemplary embodiment, the liquid metal has abulk thermal conductivity between 7 and 100 W/mK. Furthermore, thethermal impedance may be low even when the semiconductor dies havedifferent thicknesses or if surfaces of two semiconductor dies that arein contact with the liquid metal are in different planes.

This improved thermal coupling may facilitate operation of thesemiconductor die at elevated temperatures and/or high power. Moreover,the liquid metal may facilitate improved thermal coupling at ambient orat low pressures (i.e., pressures below atmospheric pressure), therebysimplifying and reducing the cost of a chip package (such as theapparatus) that includes the one or more semiconductor dies. In someembodiments, the liquid metal does not form a permanent bond with theone or more semiconductor dies, thus allowing the chip package to bereworked.

Consequently, the apparatus (and the process) described below facilitatethe use of liquid metal as the thermal-interface material, and thus, theoperation of the one or more semiconductor dies at high thermal loads.Moreover, by using the apparatus and/or the process, the liquid metalcan be dispensed and contained in a controlled manner, without damagingthe components, and without increasing the complexity and/or the costassociated with manufacturing the chip package.

We now describe embodiments of an apparatus that includes athermal-interface material. FIG. 1 presents a block diagram illustratingan embodiment of a chip package 100. This chip package includes at leastone semiconductor die, such as semiconductor die 110, and a heat-removaldevice 112. During operation of the chip package 100, heat is generatedby electrical circuits and/or components on the semiconductor die 110.To improve the thermal coupling between the heat-removal device 112 andthe semiconductor die 110 (and thus, to improve the transport of heatfrom the semiconductor die 110 to the heat-removal device 112) a thermalinterface including a thermal-interface material 114 having a thickness116 may be included between a surface of the semiconductor die 110 and asurface of the heat-removal device 112. In an exemplary embodiment, thethickness 116 is between 1-150 μm at atmospheric pressure or at acontact pressure of 5 psi.

As noted previously and discussed further below, the thermal-interfacematerial 114 may be a liquid (i.e., a material without shear strength)at room temperature and/or an operating temperature (such as 80, 100, or125 C) of the semiconductor die 110. Consequently, a gasket 118 may bemechanically coupled and/or chemically coupled to the semiconductor die110 and the heat-removal device 112 in the chip package 100, both tocontain the liquid thermal-interface material 114 and to protect it fromcontamination. Note that there may be a void (indicated by the hatchedregion) between the thermal-interface material 114 and the gasket 118.

In principle, a wide variety of thermal-interface materials may be usedto provide the thermal interface. However, many existingthermal-interface materials have melting points above room temperature.Note that existing thermal-interface materials include: conventionalheat-sink grease (such as silicone-based grease), thermally conductivepads, phase-change materials (such as wax-based materials),heat-transfer fluids (such as ethylene glycol or propylene glycol),water, or thermally conductive solders (such as commercially pureindium). As discussed below, low-melting point metal alloys (such as aliquid metal that has a melting-point below room temperature or 25 C)have superior physical properties that may facilitate improved operationof the one or more semiconductor dies.

In particular, the physical properties of these metal alloys enable themto conform to the surfaces of the one or more semiconductor dies, evenif the semiconductor dies have different thicknesses and/or havesurfaces that are not coplanar. Consequently, thermal boundaryresistances associated with low-melting point metal alloys may be small.

Moreover, low-melting point metal alloys have high bulk thermalconductivities, which, in conjunction with the low boundary resistances,may result in a low thermal resistance between the semiconductor die 110and the heat-removal device 112. In turn, a low thermal resistance mayreduce the sensitivity to changes in the thickness 116 of thethermal-interface material 114 (which is also referred to as a bond-linethickness). For example, the thermal-interface material 114 may have abulk thermal conductivity between 7 and 100 W/mK and the thermalresistance of the thermal interface may be less than 0.2 K/W.Consequently, a thermal difference or gradient ΔT between thesemiconductor die 110 and the heat-removal device 112 may besignificantly reduced or eliminated relative to the thermal gradientassociated with other thermal-interface materials. Furthermore, becausethe metal alloys are already liquid at the operating temperatures of theone or more semiconductor dies, the thermal-interface material 114 willnot be near a critical thermal breakdown temperature.

In some embodiments, the liquid metal is configured such that apermanent chemical bond does not occur with the semiconductor die 110and/or the heat-removal device 112. This property facilitates easiercleaning of these components (for example, using a vacuum, a mechanicalwipe, and/or a cleaning agent, such as acetone and/or isopropyl alcohol)and/or rework of the chip package 100.

In some embodiments, the thermal-interface material 114 in the thermalinterfaces includes: bismuth, lead, zinc, sliver, gold, tin, chromium,nickel, aluminum, palladium, platinum, tantalum, gallium, indium, and/ortitanium. For example, the thermal-interface material 114 may includemetallic particles of one or more of the preceding materials. In someembodiments, the thermal-interface material 114 is an alloy thatincludes 1, 2, 3, or more metal elements. In some embodiments, thethermal-interface material 114 is a eutectic material. Moreover, in someembodiments the liquid metal may be doped with other materials, such asdiamond and/or graphite. These materials may increase or enhanceinterfacial adhesion between the liquid metal and the semiconductor die110 and the heat-removal device 112. In general, the liquid metal mayinclude a variety of organic and/or inorganic compounds.

In an exemplary embodiment, the liquid metal is an alloy that includesgallium, indium, and tin (or a similar density liquid metal). This alloycan be formulated in a variety of compositions, including eutecticgallium-indium-tin alloy (62.5% gallium, 21.5% indium, and 16.0% tin)with a melting point of 10.7 C and Galinstan™ (68.5% gallium, 21.5%indium, and 10.0% tin) with a melting point of around 22 C. In someembodiments, the gallium-indium-tin alloy includes between 55-75%gallium, 15-25% indium, and 5-20% tin. In another embodiment, thethermal-interface material 114 includes 75.5% gallium and 15.7% indium,with a melting temperature of 15.7 C, or 62.5% gallium, 21.5% indium,and 10.7% tin, with a melting temperature of 10.7 C.

Note that in some embodiments chip package 100 includes fewer oradditional components. Moreover, two or more components are combinedinto a single component, and/or a position of one or more components maybe changed.

We now discuss embodiments of a method for applying a thermal-interfacematerial, such as the thermal-interface material 114, to one or moresurfaces of the semiconductor die 110 and/or the heat-removal device112. FIG. 2A presents a block diagram 200 illustrating an embodiment ofa portion of a process for applying the thermal-interface material 114(FIG. 1). During this process, one or more semiconductor dies, such assemiconductor die 110, and/or heat-removal device 112 may be attached toone or more carriers, such as carrier 210. This carrier facilitatestransportation of the components during the manufacturing process andprotects the components from corrosion by the thermal-interface material114 (FIG. 1).

Moreover, the carrier 210 may allow the tooling in the remainder of theprocess to be common, i.e., to be used with any of the components. Whilenot shown, the carrier 210 may include alignment features, which may beused to position one or more masks relative to the components (asdiscussed further below with reference to FIGS. 2B and 2C). In someembodiments, a surface 212 of the carrier 210 is coplanar with surfaces214 of the components that will be coated with the thermal-interfacematerial 114 (FIG. 1).

Carrier 210 may include a material that resists corrosion by thethermal-interface material 114 (FIG. 1). In some embodiments, thecarrier 210 includes: stainless steel, steel, polycarbonate, and/or achemically inert material.

In order to achieve uniform and complete coverage of the desiredportions of the surfaces 214, either or both of these surfaces may beprepared by plating an initial layer onto these surfaces 214. Forexample, a nickel-copper layer may be plated onto the semiconductor die.

Then, one or more additional layers or films may be deposited and/oradhered to either or both of the surfaces 214. This is shown in FIG. 2B,which presents a block diagram 220 illustrating an embodiment of aportion of a process for applying the thermal-interface material 114(FIG. 1). In particular, a layer including an insoluble material 230that will not dissolve in the presence of the thermal-interface material114 (FIG. 1) may be deposited and another layer that includes a wettingmaterial 234 (i.e., a material that will wet with the thermal-interfacematerial 114 in FIG. 1) may be deposited above the layer. In someembodiments, yet another layer that includes an optional inter-metalliccompound 232 may be deposited between these layers.

In general, the layers shown in block diagram 220 include a metal (ormore generally, a metal alloy), such as gold, platinum, tantalum,titanium, tin, chromium, nickel, zinc, silver, and/or aluminum.Moreover, in some embodiments the layers may include an adhesionpromoter, such as an RCA-1 surface preparation and/or a silatedpromoter.

In an exemplary embodiment, the insoluble material 230 includestitanium, the wetting material 234 includes gold, and the optionalinter-metallic compound 232 includes a gold-titanium alloy. Moreover, athickness of the layer of insoluble material 230 may be 300 nm, athickness of the layer of wetting material 234 may be between 10-300 nm,and a thickness of the layer of optional inter-metallic compound 232maybe less than 100 nm.

Note that a variety of techniques may be used to deposit these layers,including: plating, evaporation, and/or sputtering. Moreover, prior tothis operation the underlying surface may be intentionally roughened(for example, using electromechanical polishing) to promote adhesion.

In an exemplary embodiment, deposition of the insoluble material 230,the wetting material 234, and/or the optional inter-metallic compound232 includes sputtering. Regions on the surfaces 214 (FIG. 2A) that areto be coated may be defined using a shadow mask. This mask may have anedge tolerance of 0.5 mm.

However, in other embodiments at least some of the layers may be adheredinstead of deposited onto the surfaces 214 (FIG. 2A). For example, apre-existing titanium film on a polymer backing may be applied andadhered to the semiconductor die 110 and/or the heat-removal device 212using epoxy or a resin cement, such as M-bond from Tokuyama America,Inc., in Burlingame, Calif. In some embodiments, these films may becarefully pressed on, for example, using a backing and low pressure.

After the one or more layers have been deposited and/or adhered to thesemiconductor die 110 and/or the heat-removal device 212, the resultingsurfaces may be burnished or polished to reduced roughness. Moreover,these surfaces may be cleaned using chemicals, such as acetone and/orisopropyl alcohol.

Next, regions where the thermal-interface material 114 (FIG. 1) is to beapplied may be defined by adhering one or more masks (such as a contactmask) onto the semiconductor die 110 and/or the heat-removal device 212.This is shown in FIG. 2C, which presents a block diagram 240illustrating an embodiment of a portion of a process for applying thethermal-interface material 114 (FIG. 1). In particular, mask 254 may beadhered to a surface 252 of a component 250 (such as the semiconductordie 110 or the heat-removal device 212 in FIG. 2B) and/or the carrier210, thereby creating a bridge between the component 250 and the carrier210, which may help hold the component 250 to the carrier 210. This mask254 may limit an area or region 258 where the thermal-interface material114 (FIG. 1) is applied (as discussed further below with reference toFIG. 2D). As noted previously, the position of the mask 254 may, atleast in part, be determined by alignment features on the carrier 210.

In an exemplary embodiment, mask 254 includes a multi-layer structure.This is shown in FIG. 3, which presents a block diagram illustrating anembodiment of a mask 300 for use during a process for applying thethermal-interface material 114 (FIG. 1). This mask includes layers withnon-adhesive material 310 (such as paper and/or Mylar®) sandwiching anadhesive material 312 (such as a rubber-based adhesive and/or anacrylic-based adhesive). In some embodiments, the non-adhesive material310 includes: 3M 7731FL, 3M FP024502, 3M 7113, 3M 7816, 3M 76999, 3M7812, and/or 3M 7600 (from 3M Corporation, in St. Paul, Minn.)Alternatively, the non-adhesive material 310 may include: Bay AreaLabels (BAL) 9415 A-10, BAL K22, BAL V23, BAL KX04, BAL P66, BAL P07,BAL K10-8, BAL K47, BAL P05, BAL K72-8, BAL M81-1.5, BAL P03, BAL K85,and/or BAL V86-4 (from Bay Area Labels, Inc., in San Jose, Calif.).

Adhesive material 312 may form a temporary or a permanent bond, and mayhave a high pull strength or a low pull strength. In general, theadhesive material 312 is chosen so that it does not leave a residue onthe surface 252 (FIG. 2C) and will not to disturb thermal-interfacematerial 114 (FIG. 1) when the mask 300 is removed. Moreover, gaps maybe defined in at least one of the layers in the mask 300, leavingexposed regions, such as exposed region 314. These exposed regions ofadhesive may adhere to the carrier 210 (FIG. 2C) and/or the component250 (FIG. 2C).

Referring back to FIG. 2C, the geometry of the exposed regions may beselected so that the thermal-interface material 114 (FIG. 1) does notleak under the mask 254 and so that the thermal-interface material 114(FIG. 1) is not moved or disturbed when the mask 254 is removed afterthe thermal-interface material 114 (FIG. 1) is applied (which isdiscussed below with reference to FIG. 2D). In some embodiments, atamp-down fixture, such as a gasket, is used to push down on theadhesive in the exposed regions with a uniform pressure, therebyproperly adhering the mask 254 to the carrier 210 and/or the component250.

In some embodiments, a region, such as corner region 256, of the mask254 may have more exposed regions, i.e., more adhesion between theadhesive material 312 (FIG. 3) and the component 250. This may reduce oreliminate disturbance of the thermal-interface material 114 (FIG. 1)when the mask 254 is subsequently removed.

Having prepared the surfaces 214 (FIG. 2A) and defined regions, such asregion 258, the thermal-interface material 114 (FIG. 1) may be appliedto the semiconductor die 110 (FIG. 2B) and/or the heat-removal device112 (FIG. 2B). This is shown in FIG. 2D, which presents a block diagram270 illustrating an embodiment of a portion of a process for applyingthe thermal-interface material 114 (FIG. 1). During this portion of theprocess, one or more carriers and/or components (such as thesemiconductor die 110 and/or the heat-removal device 112 in FIG. 2B) maybe placed into a containment box (not shown). In conjunction with themask 254 (FIG. 2C), this containment box protects corrosion-sensitivecontact pads on the components from exposure to the thermal-interfacematerial 114 (FIG. 1). In particular, only the mask 254 (FIG. 2C) andregions, such as region 258 (FIG. 2C), are exposed, and the mask 254(FIG. 2C) may ensure that the applied thermal-interface material 114(FIG. 1) is confined to these regions. In an exemplary embodiment, thecontainment box includes stainless steel, steel, and/or nickel.Moreover, in some embodiments the containment box includes an integratedfluid recovery system (to recycle excess material) and/or replaceablegaskets.

As discussed previously, the thermal-interface material 114 (FIG. 1)applied may be a metal alloy, such as a gallium-indium-tin eutectic.Component materials in this metal alloy may have a purity of 99.99% orbetter. These component materials may be mixed at 150 C with acomposition tolerance of 0.5%. Note that the component materials may beobtained from a variety of suppliers, including Alfa Acsar, Inc., inWard Hill, Mass. Alternatively, the metal alloy may be purchasedpre-mixed from suppliers, such as AIM Specialty Alloys, Inc., inCranston, R.I.

In order to obtain the desired physical properties, the appliedthermal-interface material 114 (FIG. 1) should be thin (with a thickness116 in FIG. 1 between 1-150 μm), and should uniformly and completelycover the regions, such as the region 258 (FIG. 2C). Moreover, in orderto reduce the manufacturing cost, the process of applying thethermal-interface material 114 (FIG. 1) should avoid waste (for example,by not applying excess material) and should offer high volume and highyield.

However, many liquid metals tend to bead on many surfaces. To avoidthis, an atomization process may be used to provide energy to initiatewetting with the surfaces 214 (FIG. 2A) of the component 250. As shownin block diagram 270, nozzle 280 provides a spray 282 that spray coatsthe thermal-interface material 114 (FIG. 1) onto the regions (such asregion 258 in FIG. 2C) defined by the mask 254. In some embodiments, araster pattern (which includes a sequence of parallel deposition paths)is used to reduce or minimize the amount of the thermal-interfacematerial 114 (FIG. 1) used and to obtain a uniform coverage.

During application of the thermal-interface material 114 (FIG. 1), thethermal-interface material 114 (FIG. 1) may be injected into adeposition chamber through an extended spray valve using a cartridge anda pressure between 8-12 psi. This cartridge may have a threadedconnector to couple to the deposition chamber and may include a dualplunger to prevent leakage. In some embodiments, the cartridge includesa material resistant to corrosion, such as high-density polyethylene,stainless steel, and/or nickel. Moreover, the spray valve may utilize adesign described in U.S. Pat. No. 6,523,757, entitled “Compact SprayValve,” the contents of which are hereby incorporated by reference.

As the thermal-interface material 114 (FIG. 1) is pushed through thespray valve, a sequence of bubbles are formed. An atomizing gas strikesthese bubbles, blowing them apart and atomizing the thermal-interfacematerial 114 (FIG. 1) and producing the spray 282. In an exemplaryembodiment, the nozzle 280 is 8-10 mm from the component 250 and thecartridge and spray valve are heated to 35-40 C. Moreover, the atomizinggas may nitrogen with a pressure between 10-13 psi, the raster speed maybe between 100-200 mm/s, and the deposition rate may be 12 mg/s.

Note that the amount of material applied may be monitored to ensureproper coverage and to prevent overflow. In some embodiments, thismonitoring includes visual inspection (for example, looking for pinholes and/or determining the transparency of the film) and/or weighingthe applied thermal-interface material 114 (FIG. 1). In an exemplaryembodiment, 50 mg of liquid metal are applied to the surface of a givencomponent, such as the component 250.

While spray coating has been described as an illustrative example, inother embodiments other techniques may be used separately or inconjunction with spray coating, including print-head technology and/orsilk screening. Moreover, a variety of techniques may be used to spreadthe thermal-interface material 114 (FIG. 1) and improve the uniformityof the thickness 116 (FIG. 1), including: angular acceleration (forexample, by spinning the component 250), magnetic hydrodynamics (wherecurrent in the thermal-interface material 114 in FIG. 1 generates amagnetic field that propels it in the region 258 in FIG. 2C),ultrasound, and/or mechanical vibration. In some embodiments, anintegrated sonicator, which floats on the thermal-interface material 114(FIG. 1) during or after deposition, is used to improve the uniformityof the thickness 116 (FIG. 1). In other embodiments, thethermal-interface material 114 (FIG. 1) is applied as a solid, whichbecomes a liquid at an operating temperature of the semiconductor die110 (FIG. 1).

Note that in some embodiments block diagrams 200 (FIG. 2A), 220 (FIG.2B), 240 (FIG. 2C), and/or 270, as well as mask 300 (FIG. 3), includefewer or additional components. Moreover, two or more components arecombined into a single component, and/or a position of one or morecomponents may be changed.

After the thermal-interface material is applied, mask 254 (FIG. 2D) maybe removed. Next, the semiconductor die 110 (FIG. 2B) and theheat-removal device 112 (FIG. 2B) may be assembled with a boundarymaterial (such as a gasket) in a chip package, such as the chip package110 (FIG. 1). In particular, grease, such as Krytox® (from DuPont™, inWilmington, Del.), may be applied to the heat-removal device 112 (FIG.2B), and a gasket may be picked and placed onto the heat-removal device112 (FIG. 2B). Then, grease may be applied to the top of the gasket, andthe semiconductor die 110 (FIG. 2B) may be picked and placed onto thegasket. Note that placement may be based on optical and/or mechanicalalignment features, such as pins and/or holes. In some embodiments, bluelight is used to enhance contrast during assembly of the chip package.

FIG. 4 presents a block diagram illustrating an embodiment of aresulting chip package 400. In this chip package, the thermal-interfacematerial 114 may be contained within a cavity defined, at least in part,by gasket 118 and layers 410, such as one or more of the layersillustrated in FIG. 2B. In some embodiments, inner surfaces of thiscavity may include a material that is resistant to corrosion by thethermal-interface material 114 and/or which has a permeability for waterthat is less than a pre-determined value, such that a water-vaportransmission ratio of the cavity is 10 μg/hr. For example, the materialmay include a metal, such as nickel, a nickel alloy, and/or stainlesssteel.

Consequently, gasket 118 may include a metal coating on an innersurface. For example, gasket 118 may be a stamped metal or ametal-coated plastic. In some embodiments, a tire-style gasket is usedto increase an overflow volume. Moreover, the gasket 118 may have a flatsurface that facilitates less stringent manufacturing and/or assemblytolerances.

In some embodiments, the cavity includes one or more desiccants 414 tofurther protect the thermal-interface material 114 from water. Thisdesiccant may include: type 3A, type 4A, type 7A, an alumina-silicadesiccant, and/or a molecular-sieve desiccant. In some embodiments,desiccant 414 is rechargeable. For example, desiccant 414 may includesilicon rubber and a molecular sieve.

In some embodiments, the chip package 400 includes one or more optionalmechanical coupling elements 416 (such as screws or springs) that aremechanically coupled to the heat-removal device 112. These optionalmechanical coupling elements 416 may couple the heat-removal device 112to another component. For example, the other component may include amotherboard, a chassis, and/or a processor in a computer.

Note that in some embodiments chip package 400 includes fewer oradditional components. Moreover, two or more components are combinedinto a single component, and/or a position of one or more components maybe changed.

In some embodiment, assembly of the chip module 400 occurs over a timeinterval. For example, application of the thermal-interface material 114to the semiconductor die 110 may occur at a different time thatapplication of the thermal-interface material 114 to the heat-removaldevice 112. Moreover, these components may be processed on separatefabrication lines and/or at different locations.

Consequently, there may be a need to store and protect components thatinclude the thermal-interface material 114 (for example, from watervapor) until the assembly of the chip-module 400 is completed. This maybe accomplished using a service kit, such as the storage system 500illustrated in FIG. 5A. This storage system includes one or morecontainment vessels 514 surrounding a component 510, such as thesemiconductor die 410 (FIG. 4) or the heat-removal device 412 (FIG. 4),after the thermal-interface material 114 has been applied. Thesecontainment vessels 514 may have a low permeability for water. Forexample, a given containment vessel, such as containment vessel 514-1,may include a metal-coated plastic bag. Moreover, the protection fromwater vapor may be increased by including optional desiccants 516 ineach of the containment vessels 514.

Note that containment vessels 514 effectively complete the cavitysurrounding the thermal-interface material 114. However, in otherembodiments a dummy component is used to temporarily complete the cavityuntil the assembly process with the remaining real components iscompleted. This is shown in FIG. 5B, which presents a block diagramillustrating a storage system 530 for components that incorporate aliquid metal. In particular, dummy component 512 is coupled to gasket118 by grease 412.

In an exemplary embodiment, two metal-coated plastic containment vessels514 are used to store and protect the component 510. These plasticcontainment vessels may be anti-static and the metal coating may have athickness of at least 25 μm. Moreover, optional desiccant 516-1 mayweigh 5 g and optional desiccant 516-2 may weigh 20 g. These desiccantsmay be a type 4A molecular sieve and/or a silica desiccant. In someembodiments, the containment vessels 514 are vacuum packed.

Note that in some embodiments storage systems 500 (FIG. 5A) and/or 530may include fewer or additional components. For example, the cavity instorage system 530 may include desiccants, such as desiccants 414 (FIG.4). Moreover, additional containment vessels, surrounding containmentvessels 514, may be used. Moreover, two or more components are combinedinto a single component, and/or a position of one or more components maybe changed.

The foregoing descriptions of embodiments of the present invention havebeen presented for purposes of illustration and description only. Theyare not intended to be exhaustive or to limit the present invention tothe forms disclosed. Accordingly, many modifications and variations willbe apparent to practitioners skilled in the art. Additionally, the abovedisclosure is not intended to limit the present invention. The scope ofthe present invention is defined by the appended claims.

1. An apparatus, comprising: a containment vessel enclosing a desiccantand a device, wherein the device includes: a layer mechanically coupledto a component, wherein the component can be one of a semiconductor dieand a heat-removal device; a thermal-interface material coupled to aregion of the layer; and a boundary material mechanically coupled to thelayer, wherein a perimeter defined by the boundary-material surroundsthe region.
 2. The apparatus of claim 1, further comprising an exteriorcontainment vessel enclosing the containment vessel.
 3. The apparatus ofclaim 1, further comprising another desiccant within the exteriorcontainment vessel but outside of the containment vessel.
 4. Theapparatus of claim 1, wherein the thermal-interface material includes amaterial that is a liquid metal over a range of operating temperaturesof the semiconductor die.
 5. The apparatus of claim 1, wherein at leastone of the layer and an inner surface of the boundary material includesa material that is resistant to corrosion by the thermal-interfacematerial.
 6. The apparatus of claim 5, wherein the material includes ametal.
 7. The apparatus of claim 5, wherein the material includesnickel, a nickel alloy, or stainless steel.
 8. The apparatus of claim 1,wherein at least one of the layer and an inner surface of the boundarymaterial includes a material that has a permeability for water that isless than a pre-determined value.
 9. The apparatus of claim 1, whereinthe layer is deposited or adhered onto the component.
 10. The apparatusof claim 1, wherein the boundary material is mechanically coupled to thelayer by grease.
 11. The apparatus of claim 1, wherein the semiconductordie includes a processor.
 12. The apparatus of claim 1, wherein thethermal-interface material includes a gallium-indium-tin alloy.
 13. Anapparatus, comprising: a layer mechanically coupled to a component,wherein the component can be one of a semiconductor die and aheat-removal device; another layer mechanically coupled to anothercomponent; a thermal-interface material between the component and theother component, wherein the thermal-interface material is mechanicallycoupled to a region of the layer and to a region of the other layer; anda boundary material mechanically coupled to the layer and the otherlayer, wherein the thermal-interface material is contained in a cavitydefined, at least in part, by the layer, the boundary material, and theother layer.
 14. The apparatus of claim 13, further comprising adesiccant within the cavity.
 15. The apparatus of claim 13, wherein thethermal-interface material includes a material that is a liquid metalover a range of operating temperatures of the semiconductor die.
 16. Theapparatus of claim 13, wherein at least one of the layer, the otherlayer and an inner surface of the boundary material includes a materialthat is resistant to corrosion by the thermal-interface material. 17.The apparatus of claim 16, wherein the material includes a metal. 18.The apparatus of claim 16, wherein the material includes nickel, anickel alloy, or stainless steel.
 19. The apparatus of claim 13, whereinat least one of the layer, the other layer and an inner surface of theboundary material includes a material that has a permeability for waterthat is less than a pre-determined value.
 20. The apparatus of claim 13,wherein the layer is deposited or adhered onto the component.
 21. Theapparatus of claim 13, wherein the boundary material is mechanicallycoupled to the layer and the other layer by grease.
 22. The apparatus ofclaim 13, wherein the semiconductor die includes a processor.
 23. Theapparatus of claim 13, wherein the thermal-interface material includes agallium-indium-tin alloy.
 24. The apparatus of claim 13, furthercomprising: a containment vessel enclosing the apparatus; and adesiccant within the containment vessel.